1. Field of the Invention
The present invention relates to a turbocharger with a rotary electric machine, which can be driven by the energy of exhaust gases discharged from an internal combustion engine.
2. Description of the Related Art
There has been employed in recent years a turbocharger having an exhaust turbine which is rotatable by the energy of exhaust gases from an internal combustion engine to drive a compressor mounted on the rotatable shaft of the exhaust turbine for charging air into the internal combustion engine. Japanese Laid-Open Patent Publication No. 59-101040 discloses an engine supercharging system including a rotary electric machine mounted on the rotatable shaft of a turbocharger combined with an internal combustion engine. When the internal combustion engine rotates at a low speed, the rotary electric machine operates as an electric motor to increase the boost pressure for increasing the power output from the engine. When the internal combustion engine rotates at a high speed, the rotary electric machine operates as an electric generator to produce electric power for charging a battery. Another turbocharger for an internal combustion engine disclosed in Japanese Laid-Open Patent Publication No. 60-195329 includes a rotary electric machine mounted on the rotatable shaft of the turbocharger, the rotary electric machine being operable as an electric motor or an electric generator dependent on the operating conditions of the internal combustion engine.
For operating a rotary electric machine having a rotor with a permanent magnet, it is necessary to control the phase of electric power supplied to a stator, dependent on the rotation of the rotor, in order to operate the rotary electric machine highly efficiently.
The turbochargers disclosed in the above publications do not have any means for detecting the position of magnetic poles of the rotor which has a permanent magnet. Therefore, in the disclosed turbochargers, it is impossible to control the phase of electric power supplied to the stator dependent on the rotation of the rotor, and thus the rotary electric machine cannot efficiently be operated.
Generally, a magnetic sensor or an optical sensor is employed as a device for detecting the angular position of a rotating body. Where a magnetic sensor is used as a means for detecting the position of magnetic poles of a rotor having a permanent magnet in a rotary electric machine, it is difficult for the magnetic sensor to detect the exact angular position of the rotor. This is due to a magnetic field produced by the strong permanent magnet of the rotor or an intensive magnetic field produced by a large current flowing through the coils of the stator when the rotary electric machine is operated as an electric motor.
An optical sensor employing an optical fiber is advantageous in that it is not adversely affected by any magnetic field. However, it is disadvantageous in that it is susceptible to oil and dust, and its output signal diminishes greatly during operation over a long period of time, thus failing to accurately detect the exact angular position of the rotor.